Process for treating a metal surface and reprographic material comprising a surface so treated

ABSTRACT

THIS INVENTION RELATES TO A PROCESS FOR TREATING A METAL SURFACE, WHEREIN A SURFACE OF A METAL FOIL IS SUBJECTED TO A UNIFORM TREATMENT WITH A PLASME ARC JET, AND ALSO TO A REPROGRAPHIC MATERIAL WHICH COMPRISES A METAL SURFACE WHICH HAS BEEN TREATED ACCORDING TO THE PROCESS.

July 25, 1972 J. STROSZYNSKI 3,679,418

PROCESS FOR TREATING A METAL SURFACE AND REPROGRAPHIC MATERIALCOMPRISING A SURFACE SO TREATED 4 Filed Sept. 25. 1968 INVENTOR JOACHIMSTROSZYNSKI BY EFMMELM ATTORNEY 5 United States Patent US. C]. 96-86 5Claims ABSTRACT OF THE DISCLOSURE This invention relates to a processfor treating a metal surface, wherein a surface of a metal foil issubjected to a uniform treatment with a plasma arc jet, and also to areprographic material which comprises a metal surface which has beentreated according to the process.

In a more special application, the invention relates to a process forroughening a metallic planographic printing plate, in which process thecleaning and roughening of the metallic surface are performed in a novelmanner.

In the preparation of planographic metal printing plates, a metal foilserves as the support for the printing image. Such metallic supportsalmost invariably must be cleaned, i.e. carefully freed from traces ofgrease adhering thereto from the rolling process, and, after cleaning,roughened on the surface which is to carry the printing image.Thereafter, the printing image is produced thereon. Frequently, thesurface is modified before the printing image is applied in order toimprove the adhesion of the printing image to the surface or to increasethe hydrophilic properties of the surface, for example. Cleaning of thefoil is effected by washing or by a chemical or electrochemicaltreatment, and for roughening the foil, mechanical or also chemical orelectrochemical methods are used. Both the cleaning and the rougheningof the foil surface are timeconsuming, require washing agents or otherchemicals and are bothersome due to the necessity of removing orrecovering the washing or treating agent used. Further, it is generallynecessary to effect the cleaning and roughening of the foil surface intwo separate process steps.

The present invention provides a process in which no, or considerablyless, treating agents are required and must be removed as waste, and inwhich cleaning and roughening preferably are performed in a singleprocess step.

The process of the invention is based on the known process forroughening planographic printing plates consisting of metal foils,preferably aluminum or steel foils, in which the surface of the metalfoil is provided with a printing image after it has been roughened. Inthe process according to the invention, roughening of the surface iseffected by treatment with a plasma jet.

Plasma jet treatments have only recently been introduced into the art.Plasma jets are jets of gases of very high temperature and normally alsoof high gas speed.

Within the scope of the present invention, jets of heated gases areregarded as plasma jets which have a temperature of more than 3000 C.Preferably, the gases have temperatures between 7000 and 25,000 C. Theyare generated most advantageously by means of an electric are producedin a protective gas, e.g. an argon atmosphere, between a heat-resistantelectrode, e.g. a tungsten electrode, or a series of electrodes, on theone hand, and the web of material on the other hand. Surprisingly, itwas found that, within an appropriate time of treatment, an entirelyuniform, finely roughened surface is produced. The most suitable time oftreatment maye be easily de- Patented July 25, 1972 termined by means oftests. It depends on the conditions of processing, e.g. on the kind ofmetal foil used, on the thickness of the foil and its heat capacity, andon the temperature surrounding the foil. It has proved to be ofadvantage to cool the foil with a cooling medium during the treatment,or to place it on a support cooled with a cooling medium.

In the tests made for determining suitable process conditions, theappearance of the surface produced normally also can be referred to forjudgment, it being advisable to also examine a microscopic enlargement.Thus, when treating the surface of a crude, i.e. uncleaned, aluminumsheet with a plasma jet produced by means of an argon welding deviceprovided with a screened welding electrode, it was observed that atam'perages between 10 and 60 amperes the treated surface changed itsappearance within a very short time. Even by watching the appearance ofthe surface with the naked eye, it could be determined at whichelectrode distance, amperage, treating speed, and with which shape andposition of the electric arc electrode the surface assumed the desireduniformly matte appearance. By examining the treated surface under amicroscope, at a 275 times enlargement, it could be determined, withstill finer distinction, whether, under the process conditions employed,the action of the plasma jet was too weak or too strong. In the case oftoo weak an action, the structure impressed upon the surface of thealuminum sheet by the rolling process was still visible over the entiresurface or part of it, while in the case of too strong an action, afusion of the surface was observed which, depending on the degree ofexcessive influence, ranged from fine local melting-outs to a moltensurface of coarse-wavy structure. Thus, a fluctuation (unsteadiness) ofthe electric are also became visible as small areas where the surfacehad melted.

When uncleaned foil material is used for the process according to theinvention for the preparation of planographic printing plates, theroughening process involves a cleaning of the surface. Therefore,cleaning of the surface prior to the plasma jet treatment can bedispensed with, and, consequently, foils which have not been freed fiomthe rolling grease adhering to the surfaces are advantageously used inthe process of the invention.

In addition to the advantages already mentioned, the process of theinvention affords the possibility to combine the cleaning and rougheningprocess with a modification of the plate surface. 'If the protective gasis mixed with smaller or larger quantities of air or oxygen, a certaindegree of oxidation of the surface is caused, which, in the case ofaluminum plates, for example, results in an improved hardness of thesurface which in itself is desirable. If finely dispersed kieselguhr isintroduced into the plasma jet, silicate formation on the surface iscaused simultaneously with the cleaning and roughening efltect, whichimproves the hydrophilic properties of the surface. Further, the processof the invention offers the possibility of effecting a metallization ofthe surface, simultaneously with the roughening and, if necessary,cleaning, by introducing the finely pulverized metal into the plasmajet. In this manner, a bimetal plate is produced when the process of theinvention is combined with a copper-plating of the surface, forinstance. A particularly hard surface is obtained by metallizing withtitanium. Hard metal carbides, such as silicon carbide, also may beapplied to the treated surface by the process of the invention.

In the process for the preparation of a planographic printing plate,treatment of the metal surface is followed by the application of theprinting image to the treated surface. This process step, which is knownin many modifications, is no part of the present invention, so it is notdescribed in detail. Also in the case of the present invention, theapplication of the printing image may take place in any known manner.The following are examples of methods for applying the image, withoutany limitation to the vmethods mentioned: direct inscription or tracing;transfer printing; photomechanical reproduction, e.g. by means oflight-sensitive colloid layers, diazotype layers, or azido layers;electrophotographic reproduction; image production by imagewise heataction, e.g. by thermo-polymerization; and electrochemical andelectrolytic image production.

A particularly advantageous method for a plasma arc jet treatment of thesurface of webs of metal foils, which can be used not only for thepreparation of metal support for printing plates, but also for otherpurposes, is a further feature of the present invention. According tothis method, the upper surface of the web of metal foil is treated witha plasma are jet while the web is conveyed longitudinal in a horizontaldirection, by generating a plasma are between a series of arc electrodeson the one hand and the web of metal foil on the other hand, in a zonewhich extends transversely across the web, while supplying, in the samezone, a stream of liquid cooling medium to the lower surface of the webover its entire width, and allowing the stream of cooling medium to flowoil in a horizontal discharge channel, which extends under that portionof the web which approaches the treating zone as well as under theportion which leaves it, so that the web of metal foil is supported bythe cooling medium flowing off in the horizontal discharge channel.

. The method will be described in detail with reference to theaccompanying drawing which is a diagrammatic illustration of across-section through an apparatus for performing the method.

- A web of metal foil 3 is drawn ofi a roll 1 by coiling it to form theroll 8, with the aid of a driven winding device. in its course, the webof metal foil is deflected over the contact roll 2, guided horizontallybeneath a series of tungsten electrodes 4 mounted transversely of theweb, and then again deflected over a second, driven, contact roll 7.Between the series of electrodes 4 and the web 3 passing beneath it, aseries of electric arcs 5 is generated in a protective argon gasatmosphere. Under the horizontally conducted part of the web 3, there ispositioned a container 6 for a cooling medium, which is covevred by alid 9 having a smooth horizontal upper surface. In the zone wherethe-plasma jet is generated, there is a slot 10 in the lid. Through thisslot, cooling medium from the container 6 is caused to issue by means ofa pump (not shown). I

' Under the web of metal foil 3, the cooling medium spreads on the uppersurface of the container lid and finally flows into a collecting vessel,from which it is pumped back into the container for the cooling medium.Thus, in the zone where it is acted upon by the plasma jets, the web ofmetal foil is supported by a horizontal layer of container 6 for acooling medium, which is covered by a moves transversely over the web ofmetal foil, so that 1 the plasma arc jets act uniformly upon the foilsurface. In a further modification, the electrical contact between theweb of metal foil and the source of current may be made over the coolingmedium, provided it is electroconductive.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:

1. A process which comprises subjecting the surface of an aluminum orsteel foil web to a uniform treatment with a plasma arc jet for a timesuflicient to produce a matte appearance on said surface butinsuflicient to uniformly melt said surface, said plasma arc jet beinggenerated be tween a series of electrodes and one surface of said web ina zone extending transversely of said web while said web is conveyedtransversely of said zone, and applying a liquid cooling medium to theother surface of said web.

2. A process according to claim 1 in which the web is conveyed in ahorizontal direction and is supported by a fihn of the cooling mediumflowing on a horizontal bed.

3. A process according to claim 2 in which the cooling medium iscontinuously flowing.

4. A process according to claim 1 in which a material selected from thegroup consisting of air, oxygen, kieselguhr, a finely pulverized metalor metal carbide is introduced into the plasma jet.

5. A planographic printing plate comprising an aluminum or steel foilwhich has been subjected to a plasma jet treatment so that one surfacethereof is roughened, and a photosensitive reproduction layer on saidsurface.

References Cited UNITED STATES PATENTS 3,169,892 2/1965 Lemelson 1486.33,337,309 8/1967 Lewis et a1. 117-105.2 XR 3,372,054 3/196 Wishnie etal. 29-1912 XR 2,208,703 7/1940 Rubinstein 1o1 454 3,181,461 5/1965Fromson 101-454 3,241,486 3/1966 Greubel et a1. 101 455 3,264,508 8/1966Lai et a1. 31363 3,269,856 8/1966 Jones 117-931 XR 3,277,820 10/1966Pickard 101-454 3,335,025 8 1967 Rightmire et a1. 117-934 EDWARD G.WHITBY, Primary Examin' er US. Cl. X.R.

9633; 101-454, 456; 117-49, 71 M, 93.1 PF, 105.2, 106 C, 131; 148-6.3

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 679,418 Dated Iuly 25 1972 Inventor(s)JOaChim Stroszynski It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 3, line 13, "support" should read supports Column 3, line 17,

longitudinally "longitudinal" should read Column 3, line 44, "covevred"should read 7 covered Column 4, line 1 this line should be deleted andreplaced by: cooling liquid. Advantageously, the row of electric arcsSigned and sealed this 12th day of December 1972'.

SEAL) Attest:

ROBERT GOTI'SCHALK EDWARD M.FLETCHER,JR.

Commissioner of Patents Attesting Officer F ORM 0-1050 (10-69) n u.s,covsmmzm PRINTING OFFICE: I969 o-ass-asn

